Solid state organic light emitting diode (OLED) image display devices are of great interest as a superior flat panel digital display device. These display devices utilize current passing through thin films of organic material to generate light. The color of light emitted and the efficiency of the energy conversion from current to light are determined by the composition of the organic thin film material.
When viewed in a dark environment (little ambient radiation), a display need not be as bright as when viewed in a lighter environment (more ambient radiation). If the display device light output is recalibrated periodically, it can maintain a fixed difference between the ambient and displayed light even if the ambient light changes. This can, in turn, increase display device lifetime by reducing unnecessary display brightness in a dark environment and increase display device visibility in a bright environment.
The use of photosensors with displays to detect ambient light and adjusting the brightness of the display in response to ambient illumination is known. For example, see JP2002-297096-A, which describes a circuit for providing ambient compensation to an electroluminescent display. However, as implemented, the sensor is separate from the display and senses the light at a single point. This increases the cost, number of components, and size of the device; reduces the sensitivity of the sensor; and does not directly measure the light incident on the display itself.
It is known to integrate a light sensor on a display device for the purpose of sensing light emitted from the display device itself. See for example, U.S. Pat. No. 6,489,631 issued Dec. 3, 2002 to Young et al., which describes a display having integrated photosensors for sensing light emitted by a light emitting element of the display. However, the arrangement of the sensor coupled with a light emitter limits the size of the photosensor and its ability to sense ambient light.
There is a need therefore for an improved photosensor for the detection of ambient light within an OLED display.